Diphosphonate alkyl esters



United States Patent 3,093,672 DIPHOSPHONATE ALKYL ESTERS Lee A. Miller,Dayton, Ohio, assignor to Monsanto Chemical Company, St. Louis, Mo., acorporation of Delaware No Drawing. Filed Oct. 3, 1960, Ser. No. 59,841

2 Claims.

The present invention relates to organic compounds of phosphorus andmore particularly provides a new method of preparing carboxylatephosphonates, some of which comprise a new and valuable class of organicphosphorus compounds.

According to the invention I prepare the carboxylate phosphonates by theaddition reaction of a dialkyl phosphonate with an alkyl propiolate. Thenature of the prodin which R and Y are as above defined.

. Reaction to give (-11) appears to be favored, since even when there isused a 1:1 molar ratio of the d-ialkyl phosphonate and alkyl propiolate,a substantial quantity of the 2:1 addition product (II) is formed, plusthe 1:1 addition product (I). Apparently, the 1:1 product, i.e., thedialkyl 2-carboalkoxyvinylphosphonate, containing as it does an olefinicdouble bond which is activated by the carboxylate radical, is soreactive that it competes with the alkyl propiolate for the availabledialkyl phosphonate. The diphosphonate is thereby formed; and when theinitial reaction mixture does not contain enough dialkyl phosphonate toprovide for a theoretical yield of the diphosphonate, the reactionproduct will consist of the olefinic carboxylated monophosphonate, thesaturated carboxylated diphosphonate, and unreacted alkyl propiolate. Asthe ratio of dialkyl phosphonate to alkyl propiolat-e exceeds 1: 1,increasingly greater quantities of the diphosphonate will be formed.With a 2:1 dialkyl phosphonate to propiolate ratio, the product will bepredominantly the diphosphonate. Thus, whether the reaction is conductedwith a 1:1 or a 2:1 molar ratio of dialkyl phosphonate toalkylpropiolate, will be determined by Whether or not it is desired to obtaina substantial yield of the olefinic carboxylate phosphonate (I). Thequantity of (I) which is obtained will also be determined to some extentby the reaction conditions. Thus, a short reaction time is conducive to(I), since opportunity for subsequent conversion to (II) is therebylessened.

Accordingly, depending upon the reaction conditions, the inventionprovides a method of obtaining a mixture of carboxylated phosphonateswhich consists essentially of either the dialkyl2-carboalkoxyvinylphosphonates (I) or of the tetraalkylZ-carboalkoxy-l,l-ethylidenediphosphonates (II). The compounds (I) canbe readily separated from the compounds (I I) by. isolating proceduresknown to those skilled in the art, e.g., by fractional distillation,solvent extraction, etc.

3,093,672 Patented June 11, 1963 Dialkyl phosphonates suitable forreaction with alkyl propiolates to give the carboxylated phosphonatesare simple or mixed dialkyl phosphonates. having from 1 to 5 carbonatoms in the alkyl radical, e.g., dimethyl, diethyl, dipropyl,diisopropyl, dibutyl, di-tert-butyl, dipentyl, dii-sopentyl, ethylmethyl, butyl propyl or methyl pentyl phosphonate. Examples of theuseful propiolates are methyl, ethyl, propyl, isopropyl, isobutyl, butylor pentyl propiolate.

Reaction of the dialkyl phosphonate with the alkyl propiolate proceedsreadily at ordinary, decreased or increased temperatures and in thepresence or absence of a basic or acidic catalyst and in the presence ofan inert liquid diluent or solvent. Preferably, an organic basiccatalyst is employed. This is particularly desirable when the reactionis eifected in the pressence of a diluent. Examples of presently usefulbasic catalysts are, e.g., the heterocyclic nitrogen bases such asN-methylmorpholine, pyridine, quinoline, N-ethylpiperidine, picoline,quinaldine, 4-methylpyrimidine, or N-phenylpyrazole; the tertiary aminessuch as triethylamine, triamylarnine, tri-tert-butylamine,N,N-dimethylaniline and N-benzyl-N-methylaniline; alkylene polyaminessuch as triethylenediamine; quaternary ammonium compounds such asbenzyltrimethylammonium methoxide or tetrabutylammonium butoxide; alkalimetal alkoxides such as sodium or potassium methoxide or propoxide, etc.The quantity of catalyst to be used will depend upon the nature of thepropiolate and of the dialkyl phosphonate; obviously the more reactivemethyl or ethyl esters will require less catalyst than will the somewhatmore sluggish higher alkyl esters. Whether or not a diluent is used willlikewise regulate catalyst quantity. Also variable is the temperature atwhich reaction is eifected; for, here again must be taken intoconsideration the nature of the reactants, catalyst quantity, andwhether or not a diluent is used. The reaction is generally exothermic;hence, the present addition reactions can be conducted at ordinary roomtemperature or even at decreased temperatures, but heating of thereaction mixture may be needed to complete the reaction. All of thesevariables, i.e., catalyst quantity, use of diluent ad temperatureconditions can readily be arrived at by easy experimentation. Very rapidreaction at room temperature, as evidenced by rapid temperature rise,will show the need for a diluent and/ or lower temperature and/ or lesscatalyst. Conversely, no reaction or only a very slow reaction at roomtemperature will indicate the use of more extreme conditions, i.e.,extraneous heating and/ or no diluent and/or more catalyst. Thus,arrival at optimum reaction conditions is simply a matter of routineprocedure by one slcilled in the art.

The reaction product generally consists of the monophosphonate, i.e.,the dialkyl Z-carboalkoxyvinylphosphonate, and of the diphosphonate,i.e., the tetraalkyl Z-carboalkoxy 1,1 ethylidenediphosphonate invarying proportions. If a diluent had been employed, it-and anyunreacted, excess dialkyl phosphonate and/or alkyl propiolate areremoved by distillation, to leave as residue the mixture of saidcarboxylated monophosphonate and carboxylated diphosphonate. There issufiicient disparity, generally, in the boiling points of the two topermit separation thereof by easy fractional distillation. For somepurposes separation will not be necessary.

To recapitulate: In the preparation of the carboxylated phosphonates bythe presently provided process, the dialkyl phosphonate is mixed withthe alkyl propiolate, preferably in the presence of a basic catalyst andin the presence or absence of an inert diluent or solvent at atemperature which may range from below room temper-ature to refluxing,say, at from 0 C. to C., and the resulting mixture is allowed to standuntil formation of a carboxylate-phosphonate product has occurred. Thediaikyl phosphonate and the propiolate are employed in substantiallyequimolar proportions to obtain a mixture of the olefinic carboxylatedmonophosphonate and the saturated carboxylated diphosphonate; however,an excess of the dialkyl phosphonate may be used to obtain apreponderant quantity of the diphosphonate, or an excess of thepropiolate may be used to increase the yield of the olefiniccarboxylated monophosphonate. An excess of the propiolate may also serveas diiuent. Extraneous, inert liquid diluents which are presently usefulare, e.g., benzene, toluene, xylene, hexane, dioxane, nitrobenzene,acetone, hexachloroethane, etc.

Examples of carboxylated phosphonates which are prepared according tothe invention from the indicated dialkyl phosphonate and the indicatedalkyl propiolate are shown below:

Dimethyl 2 carbomethoxyvinylphosphonate and/or tetramethyl 2carbomethoxy-1,1-ethylidenediphosphonate from methyl propiolate anddimethyl phosphonate.

Diethyl 2-carboethoxyvinylphosphonate and/or tetraethyl 2-carboethoxy1,1 ethylidenediphosphonate from ethyl propiolate and diethylphosphonate.

Dimethyl 2-carboethoxyvinylphosphonate and/ or tetramethyl 2carboethoxy-l,1-ethylidenediphosphonate from ethyl propiolate anddimethylphosphonate.

Dibutyl 2-carbomethoxyvinylphosphonate and/ or tetrabutyl 2carbomethoxy-1,1-ethylidcnediphosphonate from dibutyl phosphonate andmethyl propiolate.

Dipentyl 2-carbopropoxyvinylphosphonate and/ or tetrapentylZ-carbopropoxy-l,l-ethylidenediphosphonate from dipentyl phosphonate andpropyl propiolate.

iDiisopropyl 2 carbomethoxyvinylphosphonate and/or tetraisopropyl 2carbomethoxy-l,l-ethylidenediphosphonate from diisopropyl phosphonateand methyl propiolate.

Ethyl methyl 2-carbobutoxyvinylphosphonate and/ or diethyl dimethylZ-carbobutoxy-l,l-ethylinenediphosphonate from ethyl methyl phosphonateand butyl propiolate.

Dipropyl 2-carbopentyloxyvinylphosphonate and/or tetrapropylZ-carbopentyloxy-l,1-ethylidenediphosphonate from dipropyl phosphonateand pentyl propiolate.

The dialkyl 2-carboalkoxyvinylphosphonates which are prepared by thepresently provided process are compounds which are useful for thepreparation of synthetic resins and plastics either byhomopoly-merization or by copolymerization with copolymerizabiemonomers, e.g., styrene, vinyl acetate, acrylonitrile, methylmethacrylate, ethyl acrylate, vinylpyrrolidone, etc. They are likewiseuseful as intermediates, e.g., for the preparation of dialkyl2-carboalkoxy-1,2-dichloroethylphosphonates by reaction with chlorine.

The presently provided tetraalkyl 2-carboalkoxy-1,1-ethylidenediphosphonates are new, well defined compounds which rangefrom viscous oils to waxy or crystalline solids. They are advantageouslyused for a variety of industrial and agricuitural purposes, e.g., asplasticizers for synthetic resins, as gasoline and lubricant additives,and as plant-growth regulators. When employed as a foliage spray oneither broad-leaf or narrow-leaf plants, at an 0.5% concentration, theyhave a growth-retarding effect thereon, but do not kill the plants.Premature cropping and unwanted exuberance of foliage is therebyprevented. When employed as additives to leaded gasoline, the presentlyprovided diphosphonates serve to inhibit spark-plug fouling.

The invention is further illustrated by, but not limited to, thefollowing examples:

4, Example 1 A mixture consisting of 8.4 g. (0.1 mole) of methylpropiolate and 50 ml. of benzene was added dropwise to a mixtureconsisting of 13.8 g. (0.1 mole) of diethyl phosphonate, 50 ml. ofbenzene and 1 ml. of 40% methanolic trimethylbenzylammonium hydroxide.The temperature of the reaction mixture rose exotherrnally to about 50C. The red-orange reaction mixture was then heated at reflux for 6 hoursto assure complete reaction. After being allowed to cool to roomtemperature it was washed first with 50 ml. of saturated, aqueousammonium chloride and 50 ml. of distilled water. The solvent was removedfrom the washed product by distillation and the residue was fractionatedvia a Vigreux column to give (I), 0.9 g., Bl. 98-99 0, comprisingdiethyl Z-carbomethoxyvinylphosphonate and (II), 5.2 g., 13.1. 100-156C. (chiefly l49156 C.)/0.4-0.5 mm. 11 1.4444, comprising tetraethyl2-carbomethoxy 1,1 ethylidenediphosphonate.

Example 2 A mixture consisting of 8.4 g. (0.1 mole) of methyl propiolateand 50 ml. of benzene was added cautiously to a mixture consisting of13.8 g. (0.1 mole) of diethyl phosphate, 50 ml. of benzene and 0.5 ml.of 40% aqueous mcthanolic trimethylbenzylammonium hydroxide. A mildexothermic reaction occurred, and the reaction mixture darkened. Afterheating at reflux for 12 hours, the solvent was removed by distillationand the residue was fractionated via a Vigreux column to give (A), afraction, Bl. 99-102" C./0.4 mm, comprising diethyl2-carbomethoxyvinylphosphonate, and (B) a fraction, Bl. -156 C. (mostly153-156 C.)/0.4 mm., 12 1.4450, comprising tetraethyl Z-carbomethoxy 1,1ethylidenediphosphonate.

Fraction B was combined with Fraction II of Example 1, and redistilledto give the substantially pure tetraethyl 2-carbomethoxy-1,lethylidenediphosphonate, B.P. 166- 167 C./0.5 mm., 11 1.4462, whichanalyzed as follows:

Found Calcd for CnHuOxPi Percent 0.... 40. 01 40. 00 Percent 11.. 7. 2::7.27 Percent l 17.06 .20

Pudovik et al.: Bull. Acad. Sci. U.S.S.R., Div. Chem. Sci, 1954, pages543-550.

Pudovik: Bull. Acad. Sci. U.S.S.R., Div. Chem. Sci. (EnglishTranslation), 1952, pages 821-824.

2. A DIPHOSPHONATE OF THE FORMULA